A reciprocating compressor currently employed in a refrigerator for home use has no variable power feature and is generally operated at a predetermined power source frequency, for example, 50 or 60 Hz in Japan.
Also, the reciprocating compressor is generally of a structure wherein a sealed housing has a low internal pressure and employs a high pressure discharge tube through which a compressed gaseous medium is discharged to the outside of the sealed housing. An example of those reciprocating compressors is disclosed in Japanese Laid-open Patent Publication (unexamined) No. 5-126044.
For further discussion of the prior art reciprocating compressor, reference will be made to FIG. 3 of the accompanying drawings. The prior art reciprocating compressor shown therein comprises a generally cylindrical sealed housing 1 accommodating therein an electrical element (not shown) including a drive motor and a compressor element 6. The compressor element 6 comprises a cylinder 2, a cylinder head 3, a reciprocating piston 4 and a cranking member 5. The sealed housing 1 includes an exhaust muffler 7 disposed at a location laterally of the cylinder 2 and a discharge tube 8 extending completely across a wall of the sealed housing 1 and soldered to the sealed housing 1 at a portion thereof which extends through the wall of the sealed housing 1. The exhaust muffler 7 and the discharge tube 8 are connected with each other by means of a generally tortuous coupling tube 9 disposed inside the sealed housing 1. The sealed housing 1 also include a coil spring 10 mounted around the tortuous coupling tube 9 for resonance suppression.
In the prior art reciprocating compressor of the structure shown in FIG. 3, the electric element is operated at a predetermined power source frequency, for example, 50 or 60 Hz in Japan. Accordingly, the drive motor forming a part of the electric element is driven at a predetermined rotational speed at all times with its rotary drive translated by the cranking member 5 into a reciprocating motion that is assumed by the reciprocating piston 4 within the cylinder 2. The reciprocating motion of the piston 4 causes a gaseous refrigerant sucked from an external supply system (not shown) to be compressed and subsequently discharged to the exhaust muffler 7 through the cylinder head 3. The compressed refrigerant in the exhaust muffler 7 flows through the coupling tube 9 and then to the outside of the sealed housing 1 through the discharge tube 8.
During the flow of the compressed refrigerant through the coupling tube 9, the coupling tube 9 is apt to generate obnoxious noise in resonance to a pulsating motion of the compressed refrigerant within the coupling tube 9 and the operating frequency of the electric element. However, generation of the obnoxious noise is suppressed by the use of the coil spring 10.
On the other hand, in the refrigerator for home use, the need has been realized to lower the output capacity during a low load operating condition to thereby minimize a power consumption. In other words, although the coupling tube 9 employed in the prior art reciprocating compressor is designed to successfully suppress resonance when the reciprocating compressor is operated at the specific frequency of 50 or 60 Hz, the prior art reciprocating compressor still has a problem associated with the resonance of the coupling tube 9 when operated at a low frequency. Therefore, no variable-capacity refrigerator for home use has yet been made available in the market.
Accordingly, the present invention is intended to provide an improved compressor having a variable power that is substantially free from the problem associated with resonance.